The present invention relates to magnetic recording technology, and more particularly to a giant magnetoresistive read head which is capable of being used at high magnetic recording densities.
Magnetoresistive (xe2x80x9cMRxe2x80x9d) heads are currently used in read heads or for reading in a composite head. FIG. 1A is a diagram of a conventional MR head 10. The MR head 10 includes a first shield 14 formed on a substrate 12. The MR head 10 also includes a first gap 16 separating a MR sensor 30 from the first shield 14. The MR head 10 also includes a pair of hard bias layers 18a and 18b. The hard bias layers 18a and 18b magnetically bias layers in the MR element 30. The MR head 10 also includes lead layers 19a and 19b, which conduct current to and from the MR element 30. A second gap 20 separates the MR sensor 30 from a second shield 22. When brought in proximity to a recording media (not shown), the MR head 10 reads data based on a change in the resistance of the MR sensor 30 due to the field of the recording media.
FIG. 1B depicts another view of the conventional MR head 10. For clarity, only a portion of the conventional MR head 10 is depicted. Also shown is the surface of the recording media 40. Thus, the air-bearing surface (ABS) is shown. Depicted in FIGS. 1B are the first shield 14, the second shield 22, the MR sensor 30 and the leads 19a and 19b. Also shown is the height of the MR sensor 30, also known as the stripe height (h).
Giant magnetoresistance (xe2x80x9cGMRxe2x80x9d) has been found to provide a higher signal for a given magnetic field. Thus, GMR is increasingly used as a mechanism for conventional higher density MR sensors 30. One MR sensor 30 which utilizes GMR to sense the magnetization stored in recording media is a conventional spin valve. FIG. 2A depicts one conventional GMR sensor 30xe2x80x2, a conventional spin valve. The conventional GMR sensor 30xe2x80x2 typically includes a seed layer 31, an antiferromagnetic (xe2x80x9cAFMxe2x80x9d) layer 32, a pinned layer 34, a spacer layer 36, a free layer 38, and a capping layer 39. The seed layer is used to ensure that the material used for the AFM layer 32 has the appropriate crystal structure and is antiferromagnetic in nature. The spacer layer 36 is a nonmagnetic metal, such as copper. The pinned layer 34 and the free layer 38 are magnetic layers, such as CoFe. The magnetization of the pinned layer 34 is pinned in place due to an exchange coupling between the AFM layer 32 and the pinned layer 34. The magnetization of the free layer 38 is free to rotate in response to the magnetic field of the recording media 40. However, note that other conventional GMR sensors, such as conventional dual spin valves, conventional synthetic spin valves, are also used.
Conventional GMR sensors 30xe2x80x2 are used in one of two configurations, current-in-plane (xe2x80x9cCIPxe2x80x9d) or current-perpendicular-to-plane (xe2x80x9cCPPxe2x80x9d). For most commercial devices, however, the CIP configuration is used. FIG. 3 depicts the CIP configuration. Only portions of the conventional GMR sensor 30xe2x80x2 as it is used in the conventional MR head 10, is depicted. Also depicted is the recording media 40. The height (h), width (w) and thickness (t) of the conventional GMR sensor 30xe2x80x2 is also shown. In the CIP configuration, current is driven parallel to the planes of the conventional GMR sensor 30xe2x80x2. Thus, the arrow 44 depicts the direction of current. The down track direction 42 is the direction in which the head is traveling. Thus, the track width of the recording media 40 lies along the direction in which current flows. The width of the conventional GMR sensor 30xe2x80x2 is set by and typically lower than the track width of the recording media 40. Note that in the CPP configuration, not shown, current is driven perpendicular to the planes of the conventional GMR sensor 30xe2x80x2. Thus, current would be parallel or antiparallel to the down track direction 42 of FIG. 3.
Use of a the GMR sensor 30xe2x80x2 in another configuration is described in U.S. Pat. No. 5,8589,753 by Ohtsuka et al. (Ohtsuka). Ohtsuka discloses the use of pairs of spin valves in which current is driven perpendicular to the surface of the recording media. In one spin valve, current is driven towards the recording media, while in the other spin valve current is driven away from the recording media. In order to drive the current, Ohtsuka couples the spin valves to the shields.
Although the conventional MR head 10 is capable of reading the recording media 40, the current trend in magnetic recording is toward higher densities. For example, it is currently desired to read recording media having a track density of thirty-five kilo-tracks-per-inch (xe2x80x9ckTPIxe2x80x9d). At these densities, the width (w) of the conventional GMR sensor 30xe2x80x2 is desired to be less than 0.5 xcexcm, which is less than the width of the conventional GMR sensor 30xe2x80x2 in current generation devices. At higher densities, the width of the conventional GMR sensor 30xe2x80x2 will be less, for example on the order of 0.2-0.3 xcexcm. At the same time, it is desirable to have a particular resistance for the sensor, typically on the order of twenty-five to forty-five Ohms. The resistance of the sensor is proportional to the length of the sensor along which the current travels and inversely proportional to the cross-sectional area through which the current passes. In the CIP configuration, depicted in FIG. 3, the resistance is proportional to the track width (w) and inversely proportional to the thickness (t) and stripe height (h). Furthermore, the thickness of the conventional GMR sensor 30xe2x80x2 cannot be radically changed. Consequently, the thickness of the conventional GMR sensor 30xe2x80x2 cannot be used as a mechanism for altering the resistance of the conventional GMR sensor 30xe2x80x2. As the track width and, therefore, the width of the conventional GMR sensor 30xe2x80x2 decrease, the stripe height must decrease to maintain approximately the same resistance. Current generation stripe heights may be on the order of 0.5 xcexcm, approximately half of the width of current generation versions of the conventional GMR sensor 30xe2x80x2. However, as discussed above, the width of the GMR sensor 30xe2x80x2 is desired to be below 0.5 xcexcm. For a sensor width of approximately 0.2-0.3 xcexcm, the stripe height would be reduced to on the order of 0.1 xcexcm in order to maintain the same resistance. Significantly shorter stripe heights may be difficult to fabricate because the conventional GMR sensor 30xe2x80x2 is typically lapped to set the stripe height. Lapping can vary by approximately 0.2 to 0.3 xcexcm. When the stripe height is desired to be less than or approximately the same as the variation induced by lapping, it may not be possible to fabricate conventional GMR sensors 30xe2x80x2 using conventional techniques. Furthermore, even if a conventional GMR sensor 30xe2x80x2 having such a small stripe height can be fabricated, heating may drastically shorten the life of the GMR sensor 30xe2x80x2. Consequently, the conventional GMR sensor 30xe2x80x2 in the conventional MR head 10 may be unsuitable for higher track densities.
Furthermore, as the stripe height of the conventional GMR sensor 30xe2x80x2 is decreased, the conventional GMR sensor 30xe2x80x2 becomes more subject to destruction due to electrostatic discharge (xe2x80x9cESDxe2x80x9d). Reducing the stripe height of the conventional GMR sensor 30xe2x80x2 renders the GMR sensor 30xe2x80x2 less able to dissipate a charge through the leads 19a and 19b (shown in FIG. 1B). Consequently, when the conventional GMR sensor 30xe2x80x2 gains an electrostatic charge, the charge is more liable to jump through one of the gaps 16 or 20 (shown in FIG. 1A) to one of the shields 14 or 22, respectively. Generally, such a discharge destroys the conventional GMR sensor 30xe2x80x2. Consequently, as the stripe height of the conventional GMR sensor decreases, the conventional GMR sensor 30xe2x80x2 becomes increasingly prone to destruction due to ESD.
There is an additional limiting factor to the height of the conventional GMR sensor 30xe2x80x2. As magnetic flux travels up the conventional GMR sensor 30xe2x80x2, away from the recording media 40, flux leaks out of the conventional GMR sensor 30xe2x80x2. The first shield 14 and second shield 22 are significantly larger than the conventional GMR sensor 30xe2x80x2. Thus, magnetic flux leaks out of the conventional GMR sensor 30xe2x80x2 and into the shields 14 and 22. The height at which virtually all of the magnetic flux has leaked out of the conventional GMR sensor 30xe2x80x2 is defined as the flux decay length. If the conventional GMR sensor 30xe2x80x2 is made longer than the flux decay length, the additional height of the conventional GMR sensor 30xe2x80x2 will contribute to the resistance, but not to the magnetoresistance. The additional height of the conventional GMR sensor 30xe2x80x2 will, therefore, be wasted. Thus, the height of the conventional GMR sensor 30xe2x80x2 should be less than the flux decay length. However, in most conventional systems, the desired resistance, discussed above, results in a significantly shorter height for the conventional GMR sensor 30xe2x80x2 than the flux decay length.
In addition, if the GMR sensor 30 is used in the CPP configuration, it is extremely difficult to fabricate, even for current generation conventional MR heads 10. The CPP configuration will also still result in a device resistance that is too low.
Accordingly, what is needed is a system and method for providing a MR head which is capable of reading information stored on magnetic recording media at higher densities. The present invention addresses such a need.
The present invention provides a method and system for providing a magnetoresistive head that reads data from a recording media. The method and system comprise providing a first shield, a second shield, a magnetoresistive sensor, and a lead. The first shield has a first end, a central portion and a second end. The first end is closer to the recording media during use than the second end. The second shield has a first end, a central portion, and a second end. The first end of the second shield is closer to the recording media during use than the second end of the second shield. The first end of the second shield is separated from the first end of the first shield by a read gap. The central portion of the second shield is separated from the central portion of the first shield by a distance that is greater than the read gap. The magnetoresistive sensor is disposed between the first shield and the second shield and has a front end and a back end. The front end of the magnetoresistive is closer to the recording media during use than the back end. The front end of the magnetoresistive sensor is electrically coupled with the first end of the first shield or the first end of the second shield. The lead is electrically coupled with the back end of the magnetoresistive sensor. Thus, current is driven through the magnetoresistive sensor in a direction substantially perpendicular to the recording media during use.
According to the system and method disclosed herein, the present invention provides a magnetoresistive head in which current is driven substantially perpendicular to the recording media and which has an increased flux decay length. The increased flux decay length can be taken advantage of because the direction in which current is driven.
Consequently, the MR head is capable of reading higher density recording media.